The human platelet derived growth factor will be further characterized by physical and chemical techniques. Peptide maps and limited sequence analysis of the isolated peptides will be done. Antibodies to the purified protein will be obtained and a radioimmunoassay for the human platelet derived growth factor developed. The human platelet derived growth factor will be radiolabeled with 125I. The binding of the labeled protein to Swiss 3T3 cells will be measured and the association constant and numbers of binding sites/cell obtained. Using a platelet derived growth factor-sepharose affinity column, attempts will be made to isolate the plaelet derived growth factor receptor on the surface of Swiss mouse 3T3 cells. Protein phosphorylation will be investigated as an early event subsequent to the binding of platelet derived growth factor to 3T3 cells. Possible phosphoproteins identified will be isolated, purified, and the specific amino acid residue modified will be identified. Additional investigations will be done in an attempt to identify the function of the phosphoproteins isolated.